The rolling-element screw device such as a ball screw and a roller screw includes a screw shaft having an outer peripheral surface provided with a helical rolling groove for rolling elements such as balls and rollers, and a nut member formed into a substantially cylindrical shape and threadedly engaged with the screw shaft through intermediation of the large number of rolling elements. Further, a load-rolling groove facing the rolling groove of the screw shaft is formed in an inner peripheral surface of the nut member. The rolling groove of the screw shaft and the load-rolling groove of the nut member face each other, with the result that a load-rolling path for the rolling elements is helically formed on a periphery of the screw shaft. Then, when the screw shaft is rotated relatively to the nut member, the rolling elements revolve around the screw shaft while rolling in the load-rolling path, with the result that the nut member performs a translational movement into an axial direction of the screw shaft.
Further, a rolling-element returning member called a return pipe or a deflector is mounted to the nut member. The rolling-element returning member has a circulation path coupling one end and another end of the load-rolling path to each other so that the rolling elements are returned from the one end to the another end of the load-rolling path through the circulation path. In other words, when the load-rolling path and the circulation path are coupled to each other, an infinite circulation path for the rolling elements is formed along the nut member.
In such a rolling-element screw device, for the purpose of preventing a life of the device from being shortened, it is necessary to supply an appropriate amount of lubricant between the rolling elements and the rolling groove of the screw shaft and between the rolling elements and the load-rolling groove of the nut member.
Conventionally, as a supply structure for a lubricant with respect to the rolling-element screw device, for example, as disclosed in JP 10-184683A, there has been known a supply structure in which lubricant applying devices are mounted at both axial ends of the nut member. Each of the applying devices includes a lubricant tank formed into a ring shape through which the screw shaft passes and mounted to the axial end portion of the nut member, and an applying body slightly projecting from an inner peripheral surface of the lubricant tank so as to come into contact with a rolling groove of the screw shaft. When the screw shaft and the nut member are rotated relatively to each other, the applying body applies a lubricant stored in the lubricant tank to the screw shaft little by little.
Meanwhile, as another supply structure for a lubricant with respect to the rolling-element screw device, there has been known a supply structure as disclosed in JP 2003-232427 A. In this supply structure, an applying body to come into contact with a rolling groove of a screw shaft is built in a rolling-element returning member. When the rolling-element returning member is mounted to the nut member, the applying body comes into contact with the rolling groove of the screw shaft. Further, a lubricant tank storing lubricant is formed into a substantially C-shape and fitted to an outside of the nut member in a manner of embracing the nut member. Coupling pipes serving as supply paths for the lubricant are arranged from the lubricant tank to the applying body built in the rolling-element returning member so that the lubricant in the lubricant tank is absorbed by the applying body through the coupling pipes.
Citation List
Patent Literature
Patent Literature 1: JP 10-184683 A
Patent Literature 2: JP 2003-232427 A